Thanks for your comments Stew.
In my earlier post (#73) I put up some pictures of the rear main bearing as used in the C1/C4 engine. I also floated the idea that even though the bearing is separately identified (by part number) for either C1 or C4 engine -perhaps they are/were interchangable. I have not yet pulled a bearing out of a crankcase to check, but I did find a sealed box labelled Continental Motors Corp, with intriguing and slightly contradictory labels, the outside indicating a C4 bearing the inside wrapping indicating a C1 bearing. See the photos.
A case of messed up packaging or strong indication about bearing interchanbability??